“If these channels, these lifelines, are not kept open, it is catastrophic for people who are already in what we have already called the world’s worst humanitarian crisis,” UN spokesman Jens Laerke said.

“Fuel, food and medicine imports must continue to enter the country. This is an access problem of colossal dimensions.”

While 17m people are short of food, the UN World Food Programme (WFP) can only reach 7m due to a lack of money and ongoing fighting.

Yemenis “hardly have food now. And if we are denied this access, even for two weeks, I can’t imagine hundreds of thousands of children’s lives are not going to be on the brink of starvation,” said WFP executive director David Beasley.

In addition, an enormous cholera epidemic has killed 2,000 people. More than half of the country’s people don’t have access to safe drinking water and even before the Saudi slaughter began in 2015 the country was one of the most parched parts of the world.

The restrictions follow Saudi accusations since the weekend that Iran supplied a missile to Yemen’s Houthi rebels that was shot down near the Saudi capital Riyadh.

Saudi Arabia has made repeated claims that Iran is arming the Houthis — often on little evidence and denied by Tehran.

Meanwhile, Saudi Arabia is armed to the teeth with British and US-made weaponry. Britain has sold billions of pounds worth of armaments, including warplanes and bombs, to the Saudis since they began pulverising Yemen in March 2015.

Up to 20,000 people have been killed and many air strikes have hit civilian targets, including hospitals and schools. Britain and the US maintain military advisers in the Saudi command centre and train the country’s air force.

The Saudi-led offensive, which involves several other regional despotisms, is an attempt to restore their man Abed Rabbo Mansour Hadi to the presidency — won unopposed in 2012 — following his ousting by the Houthis, a Zaidi Muslim religious and political movement.